Flicker elimination circuit

ABSTRACT

Flicker elimination circuitry for an electronic channel address system in a signal receiver includes an AC potential source coupled to a plurality of signal channel circuits each having a series connected diode and neon lamp connected to a DC potential source.

United States Patent Funston et al. July 8, 1975 [54] FLICKER ELIMINATION CIRCUIT 3,375,402 3/1968 Haughton 315/176 6 73 M [75] Inventors: David Lee Funston; Joseph Edward 3/19 omgomery 334/87 x Thomas, both of Batavia, NY.

[73] Assignee: GTE Sylvania Incorporated, Primary ExaminerJames B. Mullins Stamford, Conn. Attorney, Agent, or F irm-Norman J. OMalley; [22] Filed: y 31 1974 Thomas H. Buffton; Cyril A. Krenzer [21] Appl. No.: 474,870

52 U.S. Cl. 315/161; 315/133; 315/176; [571 ABSTRACT 334/86 [51] Int. Cl. HOSB 37/00 Flicker elimination circuitry for an electronic channel [58] Field of Search 315/161, 175, 176, 132, address system in a signal receiver includes an AC po- 315/ 133; 334/86, 87 tential source coupled to a plurality of signal channel circuits each having a series connected diode and [56] References Cited neon lamp connected to a DC potential source.

UNITED STATES PATENTS 2,848,685 8/1958 Mundschein 315/176 X 3 Claims, 1 Drawing Figure BAND SW1 [CH 39 39 1 FLICKER ELIMINATION CIRCUIT BACKGROUND OF THE INVENTION In electronic channel address systems for signal receivers, it has been found that neon lamps are particularly appropriate as signal channel indicating devices because of their long life, simplicity, and relatively low cost. Also, neon lamp apparatus serves as a memory device and bias source for transistors as illustrated in a copending application bearing Ser. No. 445,796, filed Feb. 25, 1974, now U.S. Pat. No. 3,859,610, and assigned to the assignee of the present application. However, it has also been found that such simple low cost indicating devices do present problems.

More specifically, it has been found that energization of the neon lamp in the signal channel of an electronic channel address system can create a most undesirable effect. For example, energization of the signal channel neon lamps from an AC potential source causes undesired detuning of the signal receiver at a 60-Hz or 120- Hz rate when varactor-type turners are utilized.

Also, neon lamps operated from a DC potential source tend to have a most undesirable flicker. In operation, the glow discharge takes place in the cathode region of the neon lamp. Since the cathode material is not perfectly homogeneous, the work function of the material lacks uniformity across the cathode. Thus, the glow discharge will form around that portion of the cathode having the lowest work function and positionally shift as the material heats up and the work function shifts. Thereupon, the glow shifts to a portion of the cathode having a lower work function and the eye perceives the shift as undesired flicker.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide an enhanced electronic channel address system for a signal receiver. Another object of the invention is to improve the signal channel indicating circuitry of an electronic channel address system. Still another object of the invention is to enhance the signal channel indicating circuitry employing neon lamps in the signal channel circuits. A further object of the invention is to eliminate the flicker of a neon lamp in the signal channel indicating circuits of an electronic channel address system.

These and other and further objects, advantages and capabilities are achieved in one aspect of the invention by a flicker elimination circuit whereby an AC potential is superimposed upon a DC potential coupled to a plurality of parallelconnected signal channels in an electronic channel address system'wherein each signal channel includes a neon lamp.

BRIEF DESCRIPTION OF THE DRAWINGS The sole FIGURE is a schematic illustration ofa preferred embodiment of the invention utilized in an electronic channel address system for a signal receiver.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, an electronic channel address system for a signal receiver includes a transformer 3 having a primary winding 5 coupled to an AC source. The secondary winding 7 of the transformer 3 is connected to circuit ground and to a rectifier 9 in the form ofa diode. The rectifier 9 provides a DC potential which is coupled by series connected resistors 11 and 13 to a plurality of parallel-coupled signal channel circuits 15, 17, and 19. Also, the rectifier 9 is coupled to circuit ground by a capacitor 10.

Each one of the plurality of signal channel circuits l5, l7, and 19 includes a diode 21, neon lamp 23, and resistor 25 series connected intermediate the DC potential available at the resistor 13 and circuit ground. A switch 27, manual in this example although remotely controlled switches as equally appropriate, connects the junction of the series connected diode 21 and neon lamp 23 of each of the signal channel circuits 15, 17, and 19 to the. junction of a capacitor 29 connected to the resistor 13 and diode 21 of each of the signal channel circuits 15, 17, and 19 and to a resistor 31 connected to the rectifier 9 and via a resistor 32 and a Zener diode 33 to circuit ground. A transistor 35 in each one of the signal channel circuits 15, 17, and 19 has a base connected to the junction of the neon lamp 23 and resistor 25; an emitter connected to circuit ground; and a collector connected to a resistor 37 coupled to bandswitching circuitry and to an adjustable resistor 39. The resistor 39 is coupled to a potential source 8+ and via a diode 41 to a tuning rail 43 for a varactor-type tuner for example.

Also, an AC potential available at the secondary winding 7 of the transformer 5 is coupled via a capacitor 45 to the junction of the series connected resistors 11 and 13. In turn, the resistor 13 is connected to the diodes 21 and via the capacitor 29 and switch 27 to the neon lamp 23 of each one of the signal channel circuits 15, 17, and 19 respectively.

As to general operation, it should perhaps be noted that the transistor 35 in the signal channel circuits 15, 17, and 19 must be maintained in a saturation condition for whichever one of the signal channels selected. Should the transistor 35 shift to a non-saturation condition, it can readily be seen that the potential applied to the adjustable resistor 39 would undesirably vary as would the potential at the tuning rail 43. Thus, undesired distortion and detuning of the tuner and signal receiver would result. i

As to operation of the flicker elimination circuitry, activation of the switch 27 of the signal channel circuit 15, for example,v causes ionization of the lamp 23 whereupon current flows through resistor 31, causing the voltage at the junction of the capacitor 29 and resistor 31 to drop. This drop in voltage at the junction of the capacitor 29 and resistor 31, which is fed by the capacitor 29, to the junction of the capacitor 29 and resistor l3 extinguishes any previously energized neon lamp 23 or signal channel circuit such as channels 17 and 19.

At the same time, an AC potential available at the output of the secondary winding 7 of the transformer 3 is coupled via the series connected capacitor 45, resistor 13, and diode 21 to the neon lamp 23. Thus, an AC potential is superimposed upon a DC potential applied to a neon lamp 23 in one of the parallel-coupled signal channel circuits 15, 17, and 19. Moreover, the applied AC potential is of a frequency greater than the human eye flicker perception frequency and 60-Hz is a preferred AC potential frequency.

As previously mentioned, the non-uniformity of the cathode material of a neon lamp causes formation of a glow around that portion of the cathode having the lowest work function. As the cathode heats, the work function at the glow portion increases and the glow shifts to another portion of the cathode materiaL This positioned shift of the glow appears as flicker to the human eye.

The human eye will perceive a low frequency blinking of a light source as flicker. As the frequency of the blinking is increased, a frequency will be reached at which the blinking or flicker is not observable. This flicker frequency is referred to as the critical fusion frequency.

This critical fusion frequency is directly related to the logarithm of luminance so that the critical fusion frequency is low for low levels of luminance. Also, the critical fusion frequency increases approximately logarithimically with increases in retinal area illumination. Thus, a comparatively low liminance source, such as a neon lamp, which appears at a normal viewing distance as a near point light source, has a relatively low critical fusion frequency.

As the glow shifts or the lamp flickers, a voltage shift occurs at the output of the neon lamp. Monitoring this voltage shift provides a measure of current needed to control the flicker. Thus, an AC current may be introduced which is substantially equal to the DC current available when the above-mentioned voltage shift occurs. Moreover, the introduced AC current is limited to the value of the abovementioned DC current occuring during the voltage shift since the neon lamp would tend to be rendered non-conductive on negative AC peak values should the AC current exceed the DC current.

Thus, injection of an AC potential super-imposed upon a DC operational potential will tend to provide a critical fusion frequency for a neon lamp. As an AC current is added, the flicker frequency increases and tends to synchronize at some frequency which is a submultiple of the injected AC frequency. Thereupon, the undesired flicker of the neon lamp will be unobservable to a viewer. Moreover, a value of AC current is selected whereby the current flow of the neon lamp is maintained at a relatively low value to enhance the life of the lamp but sufficient to raise the flicker rate above the critical fusion frequency.

Thus, there has been provided a flicker elimination circuit for neon lamps. The circuitry is especially appropriate to electronic channel address systems for signal receivers and eliminates or greatly inhibits a most undesirable and distracting flicker effect. The circuitry is inexpensive of materials, simple, and reliable. Moreover, the desired enhanced effect is achieved in a manner believed to be previously unknown and with a minimum of risk to the operation of the existing apparatus.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

What is claimed is:

1. In an electronic channel address system for a signal receiver having a plurality of parallel-coupled signal channel circuits each employing a series connected diode and neon lamp, a flicker elimination circuit comprising:

a DC potential source coupled to each one of said parallel-coupled signal channel circuits; and

an AC potential source coupled to each one of said parallel-coupled signal channel circuits, said AC potential super-imposed upon the applied DC potential and having a frequency greater than the flicker threshold of the human eye and providing an AC current not greater than the DC current provided by said DC potential source whereby discernible flicker of said neon lamp is eliminated.

2. The flicker elimination circuit of claim 1 wherein said AC potential source is at a frequency of about- Hz.

3. A flicker elimination circuit for an electronic channel address system in a signal receiver comprising:

a plurality of parallel-coupled signal channel-circuits each employing a series-connected diode and neon lamp;

a DC potential source connected to each one of said parallel-coupled signal channel circuits; and

an AC potential source connected to each one of said parallel-coupled signal channel circuits, said AC potential source having a frequency of about 60-Hz and greater than the flicker threshold of a human eye and providing an AC current equal to or less than a DC current from said DC potential source, said AC potential super-imposed upon said DC potential. 

1. In an electronic channel address system for a signal receiver having a plurality of parallel-coupled signal channel circuits each employing a series connected diode and neon lamp, a flicker elimination circuit comprising: a DC potential source coupled to each one of said parallelcoupled signal channel circuits; and an AC potential source coupled to each one of said parallelcoupled signal channel circuits, said AC potential superimposed upon the applied DC potential and having a frequency greater than the flicker threshold of the human eye and providing an AC current not greater than the DC current provided by said DC potential source whereby discernible flicker of said neon lamp is eliminated.
 2. The flicker elimination circuit of claim 1 wherein said AC potential source is at a frequency of about 60-Hz.
 3. A flicker elimination circuit for an electronic channel address system in a signal receiver comprising: a plurality of parallel-coupled signal channel-circuits each employing a series-connected diode and neon lamp; a DC potential source connected to each one of said parallel-coupled signal channel circuits; and an AC potential source connected to each one of said parallel-coupled signal channel circuits, said AC potential source having a frequency of about 60-Hz and greater than the flicker threshold of a human eye and providing an AC current equal to or leSs than a DC current from said DC potential source, said AC potential super-imposed upon said DC potential. 